1. Field of the Invention
The invention generally relates to blood collection and processing. More particularly, the invention relates to filter devices and methods for removing leukocytes from whole blood and its components before transfusion or long term storage.
2. Description of the Prior Art
Most of the whole blood collected from donors today is not itself stored and used for transfusion. Instead, the whole blood is separated into its clinically proven components. These components include packed red blood cells, platelets and plasma. The components themselves are stored individually and used to treat a multiplicity of specific conditions and disease states.
In collecting whole blood components for transfusion, it is desirable to minimize the presence of impurities or other materials that may cause undesirable side effects in the recipient. For example, to reduce the transmission of disease and non-specific frebrile reactions, it is generally considered desirable to remove substantially all of the leukocytes from whole blood prior to transfusion, storage or separation into its clinically proven components.
In blood banks and hospitals, the most common way to remove leukocytes from whole blood is by filtration using a leukodepletion filter. Currently available leukodepletion filters employ various filtration media. One type of leukodepletion filter is fabricated from multiple, non-woven pads of melt-spun, polyester fibers, wherein the mean diameter of the fibers ranges from about 0.3 to about 3.0 micrometers. Commercially, a filter of this type is available from the Asahi Corporation, under the tradename designation Sepacell R 2000.RTM..
It is well known in the industry that currently available leukodepletion filters are not effective in removing leukocytes from warm, freshly-drawn blood. To alleviate this problem, blood banks and hospitals allow blood to age 4 to 6 hours at ambient temperature or refrigerate the red cell concentrate fraction. One protocol requires that prior to filtration the red cell concentrate is held at 4.degree. C. for twenty four (24) hours. Compared to warm blood, after the blood has been cooled, these filters typically display 1 to 3 orders of magnitude greater leukocyte depletion efficiency.
It would be advantageous to provide a leukodepletion filter which removes leukocytes equally well from warm, immediately-drawn blood (fresh) as from blood which has been cooled. Furthermore, it would be advantageous if the filter had a high capacity so that units of blood containing large numbers of leukocytes could be effectively leukodepleted using a single filter.